In a semiconductor device manufacturing process, a process object such as a semiconductor wafer is subjected to various treatments such as an oxidation treatment, a diffusion treatment, and a CVD treatment. Various processing systems, for example, heat-treatment systems are used for carrying out these treatments. A vertical heat-treatment system has a transfer space (also referred to as a loading area) in which wafers are conveyed between a transporting container for containing therein a plurality of, for example, 25 wafers, and a processing vessel for performing a predetermined treatment to the wafers contained therein.
In order to prevent the growth of natural oxide films on the surfaces of the wafers in the transfer space, a great amount (250 to 400 liters per minute) of inert gas, such as a nitrogen gas, is supplied into the transfer space to establish therein an atmosphere of an oxygen concentration less than 30 ppm. A chemical filter is provided for removing organic gases from the atmosphere in the transfer space.
It has been proposed that a dry gas of a low dew point be supplied to a transfer space so as to prevent the growth of natural oxide films (see JP6-267933A, for example). A dry-type dehumidifying apparatus for generating a dry gas of a low dew point has also been proposed (see JP2000-296309A and JP63-50047A, for example).
However, when supplying nitrogen gas, a large amount of expensive nitrogen gas is required, which results not only in a high running cost of a processing system but also in a risk of oxygen deficiency. Further, it is difficult to recover a deteriorated chemical filter by removing organic matters adhered thereto. Moreover, a dry air generating apparatus has a complicated structure and thus is costly.